1. Field of the Invention
The present invention relates generally to temperature compensating circuits for varactor diodes, and more particularly, to temperature compensating circuits for varactor diode electronic tuning circuits.
2. Description of the Prior Art
A varactor diode is an electronic component whose static capacitance value is varied in a controlled fashion by a control voltage applied thereto. As such, the varactor diode is being used in numerous applications, for example, frequency multipliers, parametric amplifiers, frequency modulators, frequency sweeper circuits, electronic tuner systems, automatic frequency control circuits, automatic frequency and phase control circuits, and the like.
As is well known, the varactor diode has a negative temperature coefficient. That is to say, as the temperature of the environment surrounding the varactor is increased, the voltage drop across the anode and cathode of the varactor diode is decreased. Over certain temperature ranges the relationship between the temperature increase and voltage drop decrease is substantially linear.
When a varactor diode, for example, is used in an electronic tuner system where the frequency selected by the tuner is varied in accordance with the level of a control voltage, temperature compensation must be provided to the varactor diode so that the selected frequency does not change with temperature.
Various temperature compensation schemes have been employed to counteract the temperature sensitivity of the varactor diode, especially in the case where the varactor diode is used in an electronic tuner system. However, as is discussed in greater detail below, such conventional compensation schemes exhibit deficiencies.